We have recently shown the existence in fat cell plasma membranes of two distinct insulin binding species by the use of detergent solubilization procedures and polyacrylamide gel electrophoresis. One species (designated I) has a very high initial binding affinity (Kd of 3 x 10 to the minus 10th power M) and a Scatchard plot of the insulin binding data is curvilinear while the second species (II) has a lower affinity for insulin (Kd of 6 x 10 to the minus 9th power M) and a linear Scatchard plot. The work proposed in this application is aimed at extending these investigations by examining other insulin target organs for the presence of these insulin binding species and by attempts at further purification and characterization of the two structures. Preliminary findings suggest that the two binding species are related and that insulin promotes the conversion of species I to species II. This relationship and the factors which cause the interconversion will be studied. In addition, the effects on the binding species of insulin resistance in fat induced by various methods both in vivo and in vitro (tissue culture) will be examined. Finally attempts will be made to reconstitute the insulin binding species into artificial lipid vesicles along with the fat cell glucose transport system. Efforts will then be made to determine if addition of insulin to this reconstituted system will activate glucose transport. It is hoped that these studies will extend our basic knowledge of insulin action.